Comparing PPM and Percentages for CO2 Sensor Ranges

It is not always clear which CO2 monitoring device is the most appropriate for specific industries. The use case, use of gas and environment will usually define which gas detection device is most suitable.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

It is important to note that a wide range of carbon dioxide monitors are available, capable of detecting anywhere from 100% CO2 down to 1000 ppm (parts per million).

The selection of a sensor or monitor possessing the appropriate range of CO2 is also critical, as the narrower the range of CO2 levels to be measured, the more accurate the device or sensor will be.

A 200 ppm change will be observable on a 1000 ppm CO2 sensor, for example, but not on a 100% CO2 sensor. This article explores a number of factors that need to be considered when deciding on the most appropriate sensor or device.

Determining the Need for CO2 Monitoring

CO2 is observed and utilized in a range of examples in the environment. Examples of where it plays an important role include the release of CO2 gas during the combustion process, through exhalation and the process of photosynthesis.

The need for carbon dioxide monitoring arises in the many instances where the following may occur:

  • It is necessary to analyze the gas for research purposes
  • The presence of the gas can result in negative health impacts
  • The gas creates a hazard

While carbon dioxide is colorless, tasteless and odorless, its presence and level can be measured utilizing specific sensing technologies, usually referred to as non-dispersive infrared sensing.

These CO2 sensors facilitate the analysis of the invisible gas via the measurement of the amount of light passing through an optical filter. The level of carbon dioxide gas present is determined by the difference in measurements between the amount of light radiated by the IR lamp and the amount of IR light received by the detector.

Understanding the Difference Between PPM and Percent CO2

Sensors and measurement devices for monitoring CO2 can be split into three main categories or ranges. These are:

  • The 0 to 10000 ppm range, utilized for monitoring indoor air quality (IAQ)
  • The 5000 ppm to 5% range is often utilized for personal safety and in the beverage, agriculture, restaurant and life sciences sectors
  • The 5% - 100% range, employed in fire suppression testing, and the industrial and biological sectors 

By first identifying the most appropriate CO2 range for a specific application, it becomes easier to select the most accurate CO2 product or sensor for monitoring the presence of the gas.

Before doing this, however, it is imperative to understand the distinction between parts-per-million and percentage CO2. Carbon dioxide is regarded as a trace gas - a gas that is present in small amounts - in the atmosphere.

What is referred to as ‘fresh air’ contains a number of gases, which typically includes the following gases:

  • Nitrogen – 78.08%
  • Oxygen – 20.9%
  • Argon – 0.93%
  • Trace amounts of helium, hydrogen, carbon dioxide, methane and other gases

Atmospheric and other gases with over 1% by volume are measured as a percent, while lower volumes – for example, CO2 and other trace gases – are measured in parts-per-million by sensor manufacturers and the gas industry.

This means that 0.04% CO2 is often described as 400 parts per million (often abbreviated to ‘400 ppm’).

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

Choosing an Industry-Appropriate CO2 Range

When measuring the presence of CO2 in indoor air, parts-per-million is the most appropriate metric. Levels of CO2 above 1% (10000 ppm) are rare in nature but can be found in environments around active volcanoes and in caves. 

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

For this reason, a 2000 ppm to 10000 ppm CO2 monitor or sensor is the most appropriate choice for measuring indoor air quality (IAQ) in offices, schools and other settings.

The ASHRAE standard for ambient indoor air in occupied spaces has changed over the years, but in general, these guidelines recommend between 800 ppm and 1000 ppm of CO2. Fresh air contains around 400 ppm CO2.

Any indoor air quality sensor or monitor capable of measuring at these ranges should have the accuracy required to indicate that the CO2 threshold has exceeded the standard for indoor air quality applications.

Popular sensors in this range include the COZIR Ambient CO2 sensor and the K30 CO2 Sensor by SenseAir.

Utilized internationally by OEM manufacturers of indoor air quality devices, these sensors are also employed in outdoor air quality devices for monitoring CO2 levels. The IAQ-MAX CO2 Monitor and Data Logger is a popular desktop indoor air quality monitor.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

A CO2 sensor in the 10000 ppm range is an appropriate option for air quality verification in spaces like car parks or garages that must adhere to Occupational Safety and Health Administration (OSHA) specifications. These guidelines state that the time-weighted average (TWA) during an 8-hour working day for an employee should not surpass 5000 ppm.

Choosing an Appropriate CO2 Monitor for Personal Safety

In environments where workers or the public will be in the presence of cylinders or tanks of stored carbon dioxide, a 5% CO2 device or sensor is the most appropriate option, as a CO2 leak in an enclosed area can lead to fatalities.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

Where a CO2 cylinder or tank leaks, sensors can be utilized to trigger an alarm. The 5% CO2 range of sensors and devices are designed to adhere to NFPA, NIOSH, IFC, OSHA and NBIC requirements.

The COZIR GC-0015 0-5% CO2 sensor is an appropriate sensor for an OEM safety device around stored CO2. The Remote CO2 Storage Safety 3 Alarm is a good choice in terms of wall-mounted safety monitors. Most handheld portable devices or personal CO2 alarms employ a 5% CO2 sensor.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

These monitors and devices can be utilized in applications such as wineries, restaurants, breweries, fast-food establishments and cultivation facilities seeking to adhere to the legal standards for personal safety and CO2 monitoring regulations in their regulatory area.

Monitoring Industrial and Biological Processes: The 100% CO2 Range

Industrial and biological processes - for example, wood gasification or biological incubators - require high levels of CO2. A sensor or device in the 10-100% CO2 range is a good choice in this instance.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

The SenseAir K33 ICB or COZIR Wide-Range 20% sensors operate within this range, while the high-speed CM-1000 Multi Sampling Data Logger is a popular choice for incubation or industrial scientific applications.

Where applications require the ability to measure up to 100% CO2 - for example, controlled atmosphere storage for grains - the SprintIR GC-0018 and COZIR GC-0016 CO2 sensors are appropriate options.

Comparing PPM and Percentages for CO2 Sensor Ranges

Image Credit: CO2Meter, Inc.

The MH-100 Biological Incubator CO2 Sensor is designed to monitor carbon dioxide levels in cell incubators, facilitating ideal tissue and cell growth, typically at 5%.

The Future of CO2 Gas Monitoring

The industries surrounding the production, storage and usage of carbon dioxide change as the world around them changes. CO2Meter is continually updating its information and resources on the variety of ways CO2 gas can be utilized across various applications.

Other sectors where carbon dioxide monitoring is vital but not explored in this article include:

  • The wine industry
  • The landfill sector
  • The mining sector
  • The construction industry
  • Controlled Environment Horticulture
  • Euthanasia
  • Modified Atmospheric Storage (MAP)

The number of existing and emerging applications, plus the range of products on offer, may make it difficult to choose the most appropriate sensor or device for a particular application.

Establishing the appropriate CO2 range needed can assist in identifying the most appropriate range of sensors or products, significantly streamlining the process of finding the optimal device for a particular application.

It is vital to keep up-to-date with changes in areas such as industry applications, current regulations, device use and signs of exposure and to obtain advice on how to communicate dangers to others. Specialists from CO2Meter are on hand to assist with inquiries and to offer advice.



This information has been sourced, reviewed and adapted from materials provided by CO2Meter, Inc.

For more information on this source, please visit CO2Meter, Inc.


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